I had a similar intermittent problem with my 99' plus 8 . It would cut out when warm. It turned out to be the temperature sensor. It was telling the ecu that it was -5c so of course would pump in loads of fuel that choked the engine.
A cheap fix also - £12.87 for the sensor.
Hope this helps -
Keith

'99 Morgan+8 4.6
'35 Hudson Terraplane Sedan
'35 Hudson Teraplane Coupe
'10 Alfa Romeo Mito